1. Field of the Invention
The present invention relates to a surface-modified nanodiamond and a production method thereof. The surface-modified nanodiamond is usable in engineering applications such as materials for polishing agents and dressers adopted to chemical mechanical polishing (CMP); plating materials for corrosion-resistant electrodes adopted to fuel cells; materials for forming very hard surface coating layers typically of cutting tools; and highly heat-resistant and highly thermally conductive materials.
2. Description of the Related Art
Nanodiamonds have characteristic properties of small average particle diameters and large specific surface areas, in addition to properties inherent to diamond. Additionally, they are relatively inexpensive and are readily available.
The nanodiamonds have been produced according to an explosion process or high-temperature and high-pressure process. The explosion process yields a nano-sized diamond (nanodiamond) by explosion of trinitrotoluene and hexogen (cyclotrimethylene-trinitramine). The resulting nanodiamond obtained by this process is highly soluble in water, but contains large amounts of contaminated other carbonaceous materials such as amorphous carbon and graphite and is hard to be chemically modified on surface. In contrast, the high-temperature and high-pressure process is a process of holding a material graphite powder at a high temperature of from 800° C. to 2000° C. and a high pressure of from 1 to 10 GPa in the presence of a metal such as iron or cobalt in a hermetically sealed and pressurized vessel to thereby allow the material to undergo phase transfer directly to a diamond. The nanodiamond obtained by this process contains less amounts of contaminated other carbonaceous materials such as amorphous carbon and graphite and have uniform particle diameters, but is poor in solubility or dispersibility and dispersion stability in water and/or organic solvents. These problems retard the development of new applications of nanodiamonds.
There have been attempted to chemically modify the surfaces of nanodiamonds in order to improve the solubility and dispersibility in water and/or organic solvents (see Japanese Unexamined Patent Application Publication (JP-A) No. 2007-238411; Japanese Unexamined Patent Application Publication (JP-A) No. 2008-303104; and Japanese Unexamined Patent Application Publication (JP-A) No. 2008-150250. The resulting nanodiamonds, however, are not always satisfactorily soluble or dispersible highly stably in water and/or polar organic solvents.